Characteristics And Source Appointment Of Atmosphere Particle In Luohe In Southern Of North China Plain Based On Particle Size Distribution

The number concentration（PNC）,surface area concentration（PSC）,volume concentration（PVC）,and particle number size distribution（PNSD）of atmospheric particles are important parameters that characterize physicochemical properties of particulate matter.Long-term online observation on urban atmospheric PNSD is helpful to understand the seasonal variations of PNSD and their responses to the source emissions and meteorological parameters,and further effectively support scientific prevention and control of particle pollution.Therefore,we selected Luohe City,a city in the southern part of the North China Plain,as the study area.We collected the long-term online data of the PNSD with 14.6～661.2nm（aerodynamic diameter,the same below）and other related parameters（e.g.,meteorological conditions,trace gas concentration,and PM chemical compositions）.Based on the methods of modal fitting,backward trajectory analysis,positive matrix factorization model（PMF）and multilinear engin model（ME-2）,we analyzed the distributions of PNC at different time scales,the influencing factors of PNC,as well as the major sources of PNC.The main results and conclusions are as follows:（1）During the observation period,the PNC was mainly distributed in the range of50～200nm;the PSC was mainly distributed in the range of 100～400nm,and the PVC was distributed in the particle size greater than 250nm in Luohe.The diurnal variation of PNC showed a bimodal distribution,with peak concentrations observed at the morning and evening time.The annual average PNC was 7434#/cm³,and the seasonal average PNC was winter（12919#/cm³）>autumn（8406#/cm³）>spring（5939#/cm³）>Summer（5268#/cm³）.The Aitken mode contributed most PNC in spring,summer and autumn;however,the accumulation mode was the major contributor to PNC in winter,and the proportions of the Aitken mode and nucleation mode decreased as compared with other three seasons.The daily variations of the nucleation mode were consistent between weekends and weekdays.While the concentrations of the Aitken mode are different at noon between weekends and weekdays.The night peak of the accumulation mode of was higher during the weekends than that during the weekdays.（2）Meteorological factors have complex influences on the PNC.The total PNC were found higher at the 0～10°C range than those in other temperature ranges.Higher PNC were also found at the range of 20%～60%of relative humidity（RH）.In addition,under high RH（>60%）conditions,the PNC decreased with the increase of RH.With the joint effects of temperature and RH,the high levels of the nucleation mode were observed under the conditions of high temperature and low RH,while those of the accumulation mode and total PNC were found higher when temperature was low.The influence of wind direction on the PNC is mainly reflected in the seasonal differences of the dominant wind direction and of peak values of different modes.Stagnant weather conditions led to the high levels of PNC.Six types of air mass trajectories were obtained by backward trajectory analysis.The influences of northern air mass were mainly characterized as the increase in the levels of PM₁₀ and the nucleation mode PNC.The higher temperature under the control of air mass from southern China led to higher PM_2.5 concentrations and accumulation mode PNC,which may be related to the large amount of air pollutants carried by the air masses when passing through the urban agglomerations.Air mass from Eastern China led to higher PM_2.5 concentrations.Under the influences of different air masses,the size distributions of PNC showed bimodal distribution in spring,and unimodal distribution in other three seasons.The maximum peak sizes were observed in the Aitken mode for spring,summer and autumn,and at120nm in winter.High O₃ led to an increase of PNC with aerodynamic diameter below100nm,while high PM_2.5 led to a decrease in PNC with the nucleation mode.（3）Combined with the data of gaseous precursors,meteorological parameters,and particulate matter chemical compositions,six major source types for PNSD were identified using the PMF model,including biomass and coal combustion sources,gasoline vehicle emission sources,diesel vehicle emissions and traffic aging sources,nucleation aging sources,photochemical nucleation sources and secondary sources.The decrease in the contributions and proportions of nucleation-related sources in winter were supposed to be related to the total concentrations of urban particulate matter.The contributions of photochemical nucleation and nucleation aging sources were low in summer,which may be caused by higher wind speed and better diffusion conditions in summer.The increase in the proportions of biomass and coal combustion sources in winter was mainly related to the winter domestic heating.Traffic activities had a great impact on the PNC,but a slight impact on the PVC.The influences of wind direction on these sources were mainly caused by the differences between upwind pollution sources and the levels of gaseous precursors.The oxidation of organic matter during the process of O₃ formation is supposed to promote the new particles formation,resulting in the higher contributions of photochemical nucleation sources and nucleation aging sources during the high O₃ days.In addition,the biomass and coal combustion sources were the largest contributors to PNC during the high PM_2.5 days.Moreover,constraining the factors based on the analysis results of PMF can remove the abnormal peak patterns in certain sources of the distributions of PSC and PVC in the larger sizes.